Reusable solid rocket motors (RSRM) used for launching and controlling spacecraft for human and non-human rated flight utilize safe and arm devices to control unwanted ignition of the rocket motor. These conventional safe and arm devices include a mechanical barrier, an initiator and a so-called “booster charge” or ignitable composition. The mechanical barrier may be positioned between a so-called “safe” position and a so-called “arm and fire” position. The safe position prevents an inadvertent so-called “firing” or detonation action of the initiator from being propagated along a so-called “fire path” to the booster charge. The arm and fire position allows firing of the initiator upon receipt of a proper mechanical or electrical impulse to be propagated along the fire path to ignite the booster charge. The safe and arm device is conventionally flanged mounted into an end of the RSRM and sealed thereto with a flange gasket made from leather or other suitable material for flange gaskets. In other applications, the safe and arm device may also be directly mounted into a housing of an igniter, which is also mounted in the RSRM.
A conventional safe and arm device 900 as shown in FIG. 9 includes an actuation and monitoring assembly 902 coupled to a barrier base assembly 904 allowing for selective positioning of a mechanical barrier 906. The barrier base assembly 904 includes the mechanical barrier 906, two initiators 908, 928, electrical position switches 910 and a pellet basket 912. The actuation and monitoring assembly 902 includes an electromotive drive 914, electrical position switches 916, manual safing mechanism 918, and an in-line gear train 920 to rotationally position the mechanical barrier 906 of the barrier base assembly 904.
The barrier base assembly 904 also includes leak test ports 922 for testing or monitoring redundant shaft seals 924 located on a shaft of the mechanical barrier 906 and redundant initiator seals 926 located between each initiator 908 and 928 and the barrier base assembly 904. The seals 924, 926 help to prevent energy coming from a motor of the RSRM (not shown) from escaping through the barrier base assembly 904 during combustion, to contain energy within the barrier base assembly 904 in the event of inadvertent initiator firing and to protect the internal compartments of the barrier base assembly 904 from corrosion. A flange gasket 930, which is depicted in broken lines, provides a seal between the motor of the RSRM and the flange 931 of the safe and arm device 900. The flange gasket 930 also helps prevent energy from escaping from the motor of the RSRM during combustion. While the flange gasket 930 is highly reliable, it is desirable to monitor or verify the adequacy of the seal between the RSRM and the conventional safe and arm device 900.
In addition to being used with the motor of an RSRM, the safe and arm device 900 may be used with a jettison motor (not shown) of an aircraft or other vehicle in flight. Conventional safe and arm device 900 includes two initiators 908, 928, one of which provides single redundancy should one of the initiators fail to fire when receiving the proper mechanical or electrical impulse. Accordingly, it is also desirable to provide a safe and arm device 900 that provides further redundancy should both initiators 908, 928 fail to fire, especially when the safe and arm device 900 is used with jettison motors or other motors that necessitate increased reliability.
Further, the manual safing mechanism 918 of the actuation and monitoring assembly 902 allows a safing pin (not shown) to be installed into the manual safing mechanism 918 by rotating the mechanical barrier 906 to the safe position and then locking the safing pin into the manual safing mechanism 918. The safing pin physically prevents the mechanical barrier 906 from positioning (rotating) into the arm and fire position beyond, i.e., out of, the so-called “sure-safe” region. The sure-safe region also includes the safe position. The sure-safe region is determined by the required degrees of safety and reliability as may be defined in Naval Ordnance (NAVORD) report 2101 and the Bruceton testing procedure. Conventional wisdom with respect safety concerns and avoidance of unintentional firing by a conventional safe and arm devices, such as conventional safe and arm device 900, may require greater than five degrees of safety and reliability when the mechanical barrier 906 is positioned in the so-called “sure-safe” region. For the conventional safe and arm device 900, six degrees of safety and reliability is achieved when the mechanical barrier 906 is rotated at least 26.3 degrees away from the fire and arm position toward the safe position. In this respect, when the mechanical barrier 906 is positioned between 0 and 66 degrees, 66 and 74 degrees or 74 and 90 degrees, the safe and arm device 900 is respectively in the safe position, an unknown position or the fire and arm position. When installed properly, the safing pin ensures that the mechanical barrier 906 cannot be rotated out of the sure-safe region. However, because of tolerance between gears and mechanical engagement requirements of the manual safing mechanism 918, the mechanical barrier 906 may be rotated toward the fire and arm position approximately 30 degrees by the electromotive drive 914 of the actuation and monitoring assembly 902. While the manual safing mechanism 918 physically ensures that the mechanical barrier 906 is secured within the sure-safe region of the safe position thereby allowing the degrees of safety and reliability to be adequately maintained until the safing pin is removed, indication by sensor signal may be lost because the mechanical barrier 906 is rotated beyond the indication limits of the electrical position switches 910, 916 (conventionally set for indicating approximately 10 degrees of rotation from either the arm and fire position or the safe position). In this regard, while the safing pin is installed, the mechanical barrier 906 may be in the sure-safe region, but rotated beyond the indication capabilities of the electrical position switches 910, 916. Accordingly, it would also be of advantage to provide a safing pin and safing assembly 918 (with an accompanying gear arrangement) that limits rotation of the mechanical barrier 906 to within the rotational limits of the electrical position switches 910, 916 in order to provide positive indication (physical indication and electrical indication) of the safe position when the mechanical barrier 906 is within the sure-safe region while providing a so-called “lock” to prevent the mechanical barrier 906 from rotating into the arm and fire position even when commanded by the electromotive drive 914 of the actuation and monitoring assembly 902.
The ignitable composition of the so called “booster charge” of the safe and arm device 900 is contained between the pellet basket 912 and barrier base assembly 904. The ignitable composition may be a packet of boron potassium nitrate (BKNO3) pellets, such as a VELOSTATE™ bag with BKNO3 therein. The pellet basket 912 includes a cylindrical housing having two open ends and fastener ports for receiving retaining bolts 932 therethrough. The packet of BKNO3 pellets is received into the cylindrical housing at one open end and a diffuser plate is coupled to the other open end. The open end of the pellet basket 912 is coupled to the barrier base assembly 904 with the bolts 932. The diffuser plate allows energy from the ignitable composition, when combusting, to be axially expelled from the pellet basket 912. It is necessary to use care in properly assembling the pellet basket 912 so as to avoid loss of ignitable material. Further, to ensure that the “fire-path” through the mechanical barrier 906 is correct when positioned in the arm and fire position, the pellet basket 912 must be adequately located, aligned and secured to the booster base assembly 904. Accordingly, it would be of additional advantage to provide a safe and arm device that includes a pellet basket that is modular in design and self-contained, enabling attachment of pellet baskets containing different amounts of the ignitable composition to the booster base assembly 904. Moreover, it is also desirable to provide a pellet basket that includes a self-locating feature for ensuring proper, i.e., determinate, alignment of the fire-path between the initiator 928, mechanical barrier 906, and the pellet basket 912. Furthermore, it is desirable to provide a pellet basket that includes a modular or standardized housing that enables coupling with a booster base while allowing different amounts of ignitable composition to be inserted therein. Still, it is desirable to provide a modular housing that self contains an ignitable composition for ready attachment to the booster base and the modular housing may be designed to further enhance directed diffusion of energy therefrom when the ignitable material is combusted.